We will test the hypothesis that pimozide alters the pharmacokinetic profile of d-amphetamine in normal volunteers. Amphetamine will be given alone and following pretreatment with pimozide, and blood will be analyzed at regular intervals for amphetamine levels. Mood, psychomotor performance, heart rate, and blood pressure will be measured hourly. The time course of various amphetamine effects will be compared to the time course of drug levels in the blood.